Due to the uniform and regular porous structure, greater specific surface area and higher thermal stability, better shape-selective catalytic performance and adsorption performance, zeolite molecular sieves are widely applied in the fields such as petrochemical industry and the like. When molecular sieves are used for industrial catalysis, 100% molecular sieves generally cannot be made into the catalyst for the industrial process. Because of worse binding property and too small particle size, molecular sieves still have a strength of lower than 20 Newtons even if press-molded, so that they cannot be molded to form the catalyst directly applied in the industrial process. In addition, the manufacturing cost of molecular sieves is generally higher. If 100% molecular sieves are used as the industrial catalyst, the operation cost of the industrial process increases. The industrial process generally requests that the catalyst has a certain shape and strength so as to be adapted to the industrial reactor. As for a fixed-bed reactor, the catalyst does not need to be moved after installation, but the catalyst shall have a certain anti-crush strength to avoid breakage due to impact during the loading process and to prevent the catalyst loaded in the lower part from breakage under pressure. The breakage and pulverization of the catalyst may result in an increase of the pressure drop in the device, abnormal reaction behavior, or product composition change, which are disadvantageous to the target reaction process. As for a fixed-bed reactor, because of circular flow and turbulent motion of the catalyst per se in the reactor, friction and collision between the catalyst particles, between the catalyst and the reactor wall, between the catalyst and the regenerator wall, between the catalyst and the heater wall, between the catalyst and the flow pipe wall all will grind and damage the catalyst so as to escape from the reaction system in a fine powder form. Such fine powder will pollute the environment, and increase the use-cost of the catalyst. Thus, no matter whether the molecular sieves are applied in a fixed-bed reactor or a fluidized-bed reactor, a binder is necessary for a catalyst composition formed by molecular sieves and carrier materials. Such molecular sieve composition has the catalytic activity, selectivity, stability, shape and strength, and meets the requirements on the catalyst during the industrial process.
Since a binder shall be added for forming the molecular sieves, and the binder wraps the molecular sieves in the molded catalyst, the effective availability of molecular sieves decreases, so as to result in a lower specific surface area and a lower activity of the catalyst. Random porous structure of the binder causes the difficulty of the dispersion of the reaction materials and product in the catalyst, and carbon deposit easily occurs, so as to have effect on the service life of the catalyst. The conversion of the binder in the catalyst into the effective component molecular sieve can overcome said problems and improve the activity and diffusivity of the catalyst.
The binderless molecular sieve catalyst involves converting the binder added during the molding of the zeolite molecular sieve catalyst into the effective component of the molecular sieve, making the whole catalyst containing no binder component and maintaining a better strength of the catalyst. In the binderless molecular sieve catalyst, the binder is completely converted to the molecular sieve component, which increases the molecular sieve content in a unit volume of the catalyst, so as to improve the activity and handling capacity of the catalyst. Meanwhile, since the catalyst contains no binder, it solves the problems that the effective availability of the molecular sieve is reduced because the binder wraps the molecular sieves, and that the binder blocks up the pore channel of the molecular sieves, so as to greatly increase the effective availability and carbon deposit resistance thereof.
Generally, a binderless molecular sieve catalyst means that the binder content in the catalyst is less than 10%.
US6509290 discloses a process for preparing a molecular sieve catalyst, which contains molecular sieve-containing attrition particles and virgin molecular sieve, the attrition particles having been recycled from a catalyst manufacture process or from a reaction system. Such process comprises mixing together molecular sieves, virgin binder and filler, spray-dried attrition particles or agglomerates, and non-virgin attrition particles from a reaction system, drying the mixture to form an end product catalyst particles. In order to increase the strength of the catalyst particles, the attrition particles substantially contain no coke.
US6153552 studies a process for preparing a molecular sieve catalyst, comprising mixing together molecular sieves and an alumina sol which is prepared in a solution and maintains a pH value of 2-10, spray-drying and calcining such mixture at high temperature, to form a catalyst resistant to attrition.
CN1791463 discloses a process for preparing a molecular sieve catalyst, comprising mixing together molecular sieve, liquid, and an effective hardening amount of a dried molecular sieve catalyst to form a slurry, drying the slurry and then calcining to form a catalyst resistant to attrition.
Although some patents have involved the process for preparing a fluidized-bed catalyst, the abrasion resistance thereof is lower and needs to be further improved.
Generally, molecular sieves are prepared by the hydrothermal synthesis, showing a powder form, having no strength, and being easy to lose. Even if they are molded by compression, the strength thereof is also less than 20 Newton, so that they cannot be applied directly. The molecular sieves shall be extruded or spray-molded by adding a binder during the industrial or laboratory application. During the molding process of the conventional molecular sieve catalyst, the weight of the binder to be added is not less than 40% of the total weight of the catalyst. Although the molded catalyst has a certain strength, it has a reduced effective availability and worse activity and diffusivity.